Bacterial oxidation has been used for a number of years in successfully processing arsenopyrite, pyrite, pyrrhotite, covellite and chalcocite ores and concentrates, the one exception to this processing has been the oxidation of chalcopyrite (CuFeS2) ores and concentrates.
Prior art mixes of bacteria used to facilitate oxidation of sulphide ores and concentrates, other than chalcopyrite ores and concentrates, use a variety of suites of bacteria. For example, the mixed bacterial culture employed by Gencor Limited of South Africa comprise predominantly Thiobacillus ferrooxidans, Thiobacillus thiooxidans and Leptospirillum ferrooxidans. The Gencor cultures consist of a mixed population of mesophilic bacteria, which operate in the temperature range of 35° C. to 45° C. (Dew & Miller, 1997).
Further, Finnish Patent Application 953488 to Gencor Limited discloses the use of Thiobacillus ferrooxidans, Thiobacillus thiooxidans and Leptospirillum ferrooxidans to achieve oxidation at a pH of preferably 3 with an ore preferably crushed to below 6 mm.
The bacterial culture utilised by BacTech (Australia) Pty Ltd, see for example U.S. Pat. No. 5,429,659, is a moderately thermophilic bacterial culture operating in the temperature range of 46° C. to 50° C. The culture has been designated “M4” by Barrett et al (1988) and has been described by Nobar et al. (1988) (Brierley and Brans 1994).
The MINBAC process developed by Mintek—Anglo American Corporation based in Randburg, South Africa utilises a mesophilic mixed bacterial culture comprising Thiobacillus ferrooxidans/Leptospirillum ferrooxidans (Brierley and Brans 1994).
The bacterial cultures presently used are unable to produce commercially acceptable results for chalcopyrite without either ultra fine milling (P80<20 μm) of the ore or concentrate to facilitate bacterial oxidation, or the use of very long leach times to achieve oxidation. Times of over 100 days are not uncommon.
Current trends are moving towards the use of higher temperatures to encourage ferric oxidation. However, the high temperatures employed lead to having to cool post-oxidation and to provide reactors formed of specialised materials, for example surgical grade stainless steel. Both circumstances increase the cost of such an operation.
The process of the present has as one object thereof to overcome the above mentioned problems associated with the prior art, or to at least provide a useful alternative thereto.
The preceding discussion of the background art is intended to facilitate an understanding of the present invention only. It should be appreciated that the discussion is not an acknowledgement or admission that any of the material referred to was part of the common general knowledge as at the priority date of the application.
Throughout this specification, unless the context requires otherwise, the word “comprise”, or variations such as “comprises” or “comprising”, will be understood to imply the inclusion of a stated integer or group of integers but not the exclusion of any other integer or group of integers.
Throughout the specification, reference to a bacterial species is to be understood to include also its sub-species.
Throughout the specification, an ore is considered material that has been removed from the ground and does not receive any treatment to increase the metal concentration. A concentrate is produced by passing an ore through a treatment process, generally gravity or flotation, in order to increase the concentration of desired metals and decrease the volume of material which is subsequently treated to recover those desired metals.